In a rehearsal room in North Hollywood are some of the battle scars Rage Against the Machine has accumulated during many years of conflict and noise. In one corner are the scorched, graffiti-covered amplifiers that bassist Tim Commerford has plugged into for nearly 20 years. At Woodstock 1999, he had the big cabinets draped with a U.S. flag, which he then soaked with lighter fluid between songs, until the final encore of "Killing in the Name."

Thousands of fans were already bouncing and shouting along to the angry, defiant chorus ("I won't do what you tell me!") when Commerford pulled out his lighter. "I lit it up, and I swear to God the flames were 20 feet in the air," he says excitedly, standing tall in olive-drab shorts and a snug T-shirt. "It was awesome — honestly, one of the most high-profile flag burnings since the Vietnam War."

Commerford, 43, is here with Brad Wilk, 42, whose kick-drum displays the band's vivid red star of revolution. And soon guitarist Tom Morello arrives, stepping into the room in a blue baseball cap for his beloved Cubs, looking up from his BlackBerry. "The show's off!" says Morello, 47, with a laugh.

The show is a big one: the L.A. Rising festival Saturday at the Los Angeles Memorial Coliseum, where Rage Against the Machine will headline a day of music and politics, with performances by Muse, Rise Against, Ms. Lauryn Hill, Immortal Technique and El Gran Silencio. Also on-site will be the festival's "Re-Education Camp," with booths for activist groups on war, poverty, labor and immigration.

In a few hours, the musicians will be joined by singer Zack de la Rocha, 41, for a full band rehearsal, as they edge closer to the festival and the band's 20th year since first jamming together in the obscurity of Sunbird Studios not far away. They are in good spirits.

"We'll be fine," says Morello casually of the practice schedule. "The first day always sounds a little bit shaky. The second day is fine. The third day it sounds like Rage Against the Machine. Fourth day it sounds exactly how it's supposed to. The fifth day sounds worse than the fourth day." He laughs. "You don't want to do seven days. You want to save it."

The band discovered its sound and mission quickly at the beginning of the '90s, mixing punk, hip-hop and hard-rock into a swirling, muscular whole. Morello's metallic guitar erupted with wild, percussive force, mimicking staccato turntable effects and channeling Jimi Hendrix with agitated riffs and blistering funk. The vocals were pure hip-hop and delivered with such furious drive by De La Rocha that they worked as a livid hard-rock roar, equal parts Black Flag and Public Enemy.

Just as crucial to the band's identity was the political content, sending radical messages on social justice to the kids via MTV and commercial radio in the form of such signature songs as "Bulls on Parade" and "Testify." (Sample lyric: "Weapons not food, not homes, not shoes / Not need, just feed the war cannibal animal.")

From stages around the planet, Rage railed against war, torture and U.S. foreign policy, and stood for abortion rights and the struggles of immigrants, farmworkers and sweatshop laborers. Riot police were often on standby outside Rage concerts, and the rockers have been regularly tear-gassed along the way. "It will definitely kick your body and your mind into overdrive when that … is going down," Wilk says.

That sound suddenly went silent in 2000, in what appeared to be an especially acrimonious and permanent breakup, just as the Bush years were set to begin. "We weren't communicating, and we were losing the friendship," says Commerford, who first met De La Rocha in grade school in Irvine. But in one of their final acts before splitting apart, the band erupted for 45 staggering minutes onstage in the "free speech" zone outside the Democratic National Convention in Los Angeles.

"Brothers and sisters, our democracy has been hijacked," De La Rocha announced to the crowd of several thousand protesters and fans, denouncing the American two-party system and what he called its collusion in political and cultural repression. Afterward, riot police descended amid a storm of rubber bullets and batons. It was a career-defining scene.

"It was one of those moments where the hair on your arms was standing up. It was really something," remembers Paul Tollett, president of Goldenvoice Productions, Rage's partner for the Coliseum show. "Rage is always there. They are a voice for people who are fed up."

And then they were gone, only reuniting years later for the Coachella Music and Arts Festival in 2007, another Goldenvoice event. "Rage Against the Machine is a political band, but it is also a band," says Morello, who graduated from Harvard with a degree in social studies and dreams of pulling on the levers of history. "Bands are sometimes fractious, and we were apart for those years. But I think it all worked out for the best.... I love and appreciate the three other guys in Rage Against the Machine now more than ever."

At rehearsal, the band is in a jovial mood, making jokes about their vintage gear as they await De La Rocha. Morello picks up a white guitar decorated with cartoon hippos. "This is the 40 Canadian-dollar pawnshop guitar. I'm not sure it's made of wood," he says with a laugh, then notes it helped win the band its first Grammy, for "Tire Me."

Morello, Commerford and Wilk formed Audioslave with vocalist Chris Cornell (Soundgarden) during the years Rage was quiet, recording three albums. In the end, they found it only made them miss their first band together. "A great thing of getting older is coming to terms and saying sorry and trying to repair damage that happened in the past," says Commerford of reuniting. "That's what we've been doing — trying to make it feel good for all of us to be here playing shows and rocking."

L.A. roots

They know Zack de la Rocha in Highland Park. He has family here, and on a recent afternoon, he is greeted at a Mexican restaurant on York Boulevard and chatted up like the regular he is.

For six years, De La Rocha and some friends ran a nearby Chicano cultural center called Regeneracion, named after a Mexican anarchist revolutionary newspaper. He orders coffee and chicken enchiladas."Good food and good politics mix in Highland Park very well," he says.

Twenty years after Rage began, the band's mission hasn't changed much. Outside the 2008 Republican National Convention in St. Paul, Minn., the band was barred by police from performing onstage for protesters but waded into the crowd to sing "Bulls on Parade" and "Killing in the Name" a capella via bullhorn.

"The unfortunate reality is that the songs I did write then are as relevant today as they were then," he says. "And I think about what it means that the songs still have life, and still have the ability to provide a necessary critique for young people to engage in. Good songs have resonance. They speak in a way that politicians don't. They speak in a way that teachers cannot."

At the Coliseum, De La Rocha hopes fans who come for the music will also be open to the groups gathered at the Re-education Camp. "Those organizations are the consciousness of the city," he says. "If young people can attend the concert and recognize they have a lot more in common with the youth in Greece and the youth of Spain and the youth that occupied Tahrir Square … than they do with the military recruiters that are entering high school campuses all over the city and their conservative teachers — then I feel we've done our job."

For selected nonprofits in the Re-Education Camp, Saturday's gathering is special. "It's huge," says Jeremy Sidell, chief development and communications officer at PATH (People Assisting the Homeless), a provider of housing and other services. "Homelessness isn't exactly a sexy cause. Events like this put issues out front and are really meaningful for us."

The same is true for the South Central Farmers, working to reclaim a 14-acre plot at 41st and Alameda that for a dozen years was set aside as a community garden. "We're going to have access to about 80,000 people. We're super-excited about this possibility to carry out our message, " says spokesman Tezozomoc.

After Coachella, Rage reentered the spotlight but shed much of the organizational baggage typical of a platinum-selling arena-rock act. They have no manager and no attorney. "The band is like local garage band that plays the Coliseum," explains Morello with a grin. "In order to make decisions, we go around on the BlackBerrys. There is no infrastructure."

The band's schedule isn't heavy and allows room for various solo projects. De La Rocha is close to finishing up an album with his other band, One Day As a Lion, and Morello releases a new album as the Nightwatchman in August. L.A. Rising is the only performance Rage has scheduled this year, and Goldenvoice is anticipating a sellout.

The setting of the festival was no accident. Rage wanted a venue that emphasized its Los Angeles identity. And the biggest room in town happened to be the eight-decade-old Coliseum, located in the heart of the city. The quartet turned to Goldenvoice Productions, the promoter not only of Coachella but of many of Rage's earliest shows. Choosing the other acts on the bill was especially important. "All the bands are pretty socially conscious," Tollett says. "That was more important to Rage than the type of music."

L.A. Rising is designed as a reflection of what the group intends to stand for. They've discussed making it an annual event. In early July, the members of Rage Against the Machine had a two-hour walk-through tour at the Coliseum to get a feel for the venue.

Standing on the field, they tossed around a football and took in the landscape. "When we first got together, we never assumed that we'd be playing anywhere other than small clubs and the garages of our friends' houses," De La Rocha says. "But one thing we realized pretty quickly was that Rage in any setting is actually made pretty intimate." Then he adds, "I don't think it's truly going to set in until that moment arrives."

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